1. Field of the Invention
The present invention relates to an inspection method and an inspection apparatus for inspecting the electrical characteristics of an inspection object. More specifically, the present invention relates to an inspection method and inspection apparatus in which contact (for example, probe) is brought into contact with the inspection object when the electrical characteristics of the inspection object are inspected.
2. Description of the Related Art
This kind of the inspection apparatus includes a loader chamber 1 for carrying an inspection object (for example, wafer) W and a prober chamber 2 for inspecting the electrical characteristics of the wafer W sent from the loader chamber 1 as shown in FIGS. 6A and 6B. The loader chamber 1 includes a cassette storage portion 3, a wafer carrying mechanism 4 for carrying the wafer W to the loader chamber 1 and a sub-chuck 5 for aligning the wafer W preliminarily. These components are controlled by a control unit (not shown).
The prober chamber 2, as shown in FIGS. 6A and 6B, includes a table (hereinafter referred to as “main chuck”) 11 on which the wafer W received from the wafer carrying mechanism 4 is mounted, an XY table 7 for moving the main chuck 11 in the horizontal direction (X and Y directions), a contact holding mechanism (hereinafter referred to as “probe card”) 12 disposed above the main chuck 11, a plurality of contacts (hereinafter referred to as “probe”) 12A of the probe card 12 and an alignment mechanism 13 for aligning a plurality of electrodes of the wafer W on the main chuck 11 with the probe.
The alignment mechanism 13 includes an upper camera 13B attached to an alignment bridge 13A and a lower camera 9C attached to the main chuck 11. As the alignment bridge 13A advances to a probe center in the center from the deep side of the front side of the prober chamber 2 along a pair of guide rails 13D, alignment of the electrodes of the wafer W with the probe 12A is carried out.
Upon alignment, the XY table 7 moves the main chuck 11 so as to lead the lower camera 9C attached to the main chuck 11 to just below the probe card 12. At this position, a lift mechanism 15B lifts the main chuck 11 and the lower camera 9C photographs a tip of a predetermined probe 12A. The control unit calculates the positional coordinates of X, Y and Z of the tip of the probe 12A from a position of the main chuck 11 at this time. Next, the alignment bridge 13A advances to the probe center and the upper camera 13B and the lower camera 9C are focused on a target 9E, so that the optical axes of both the cameras 13B, 9C are aligned. A reference position of the main chuck 11 can be obtained from the positional coordinate at this time. After that, the upper camera 13B photographs a predetermined electrode of the wafer W. The control unit calculates the positional coordinates of X, Y and Z of the electrode from the position of the main chuck 11 at this time. The electrode of the wafer W and the probe 12A are aligned based on these positional coordinates.
As shown in FIG. 6A, a test head T is disposed on the head plate 2A of the prober chamber 2 such that it may be opened and closed. The test head T and the probe card 12 are connected electrically with each other through a performance board (not shown). An inspection signal sent by a tester (not shown) to the probes 12A through the test head T and the performance board is applied to electrodes of the wafer W from the probes 12A. The electrical characteristics of a plurality of devices on the wafer W are inspected using this inspection signal.
Upon inspection, the electrodes of the wafer W is overdriven further after it comes into contact with the probe 12A and then comes into electrical contact with the probe 12A with a predetermined pressure.
At this time, a distance between the tip of the probe 12A and the electrode of the wafer W is detected at a high accuracy. By lifting the main chuck 11 just by a detected distance, the probe 12A and the electrode are brought into contact with each other securely. By overdriving the main chuck 11 from this contact position, the electrode comes into contact with the probe 12A electrically. A height of the main chuck 11 in which the probe 12A and the electrode come into contact with each other just before the overdrive is applied is called contact starting point.
According to the above-described inspection methods, the lower camera 9C of the alignment mechanism 13 photographs the tip of the probe 12A in order to obtain the contact starting point. As other inspection method, there are a method of securing electrical contact by obtaining a point in which electric conduction between the probe 12A and the electrode is started, a method of securing electrical contact after a needle trace formed by contact of the probe 12A and the electrode is inspected and the like.
As an inspection apparatus which brings an electrode into contact with the probe with electrical stability, there are an inspection apparatus described in the scope of claim for patent, paragraphs [0013], [0014] and abstract of disclosure of patent document 1 (Jpn. Pat. Appln. KOKAI Publication No. 9-51023) and an inspection apparatus described in the scope of claim for a patent, paragraph [0018] and abstract of disclosure of patent document 2 (Jpn. Pat. Appln. KOKAI Publication No. 6-163651). The semiconductor test apparatus described in the patent document 1 includes a needle drive mechanism, a pressure detection mechanism, a comparison operation control portion and a ring operation mechanism. The comparison operation control portion compares a pressure signal of the probe from the pressure detection mechanism with a reference value and the ring operation mechanism is driven based on a signal from the comparison operation control portion so as to correct an inclination of the probe ring.
The semiconductor wafer inspection apparatus described in the patent document 2 includes a pressure sensor for detecting a contact pressure between the probe and electrode and an appropriate contact pressure is secured based on a contact pressure detected by the pressure sensor.
However, according to a conventional inspection method, the lower camera 9C of the alignment mechanism 13 photographs the tip of the probe 12A from just below to detect the tip of the probe 12A as shown schematically in FIG. 7. Because the quantity of light at the tip is insufficient, a position slightly above the tip (for example, position at a needle diameter d of 5–8 μm) needs to be photographed. Thus, the position detected as the tip of the probe 12A accompanies an error of about 10 μm. The contact starting point with the electrode is difficult to detect accurately because of this error.
To search for a contact starting point in which conduction between the probe 12A and the electrode is started, the contact starting point needs to be found out accurately before the overdrive is applied to the main chuck 11. The amount of necessary overdrive fluctuates due to the condition of oxide film on the electrode surface and consequently it is difficult to obtain a stable pressure by the overdrive.
To visually inspect a probe trace on an electrode surface, the electrode needs to be overdriven in order to mark the probe trace. The height suitable for formation of the probe trace is affected by the pressure and the surface configuration of the electrode. Further, visual inspection of the probe trace varies depending on individual difference because the probe trace is very fine.
In the semiconductor test apparatus of the patent document 1, the inclination of the probe ring supporting the probe card needs to be corrected each time the electrode is brought into contact with the probe electrically.
The semiconductor wafer inspection apparatus of the patent document 2 controls a contact pressure by a pressure sensor provided on the wafer chuck. Thus, the contact pressure needs to be controlled each time the electrode is brought into contact with the probe electrically.